In recent years there has been a growing concern over exposure to toxins in the environment and food supply. The Federal Water Pollution Control Act Amendments of 1972 (P.L. 92-500) recognized the need for monitoring and establishing the presence of toxic substances in water. Organic pollutants are frequently present in very small amounts and often comprise a large number of similar compounds which may have been deposited at a particular location through a variety of means. Some of these pollutants are concentrated in the tissues of plants and animals and can be hazardous to these life forms as well as animals, including humans, that eat them. Thus the need exists for accurate measurements of trace amounts of contaminating pollutants.
While conventional chromatography and detection techniques are effective measurers and detectors of organic compounds, the samples to be tested contain the organic compound components in matrixes or are in matrixes which may interfere with the proper extraction and detection of the compound components in questions. Using conventional techniques, it has been difficult to determine certain compounds, to assess the degree of matrix effects on compound recovery and to accurately quantify the amounts of these and other compounds.
Soil, biological samples, oils and water each present their own unique difficulties and interfering chemicals. Techniques prior to, and even after, the vacuum extractor described in applicant's earlier U.S. Pat. No. 4,600,559 have not been particularly effective at detecting an accurate amount of a chemical in certain samples due to low rates of extraction and poor separation. For example, U.S. Pat. No. 4,960,711.
In the prior art, investigators have attempted to measure trace organic compounds by a number of techniques. One method is to sample gas from the head space above a sample in a closed container. The gas sample is then injected into a gas chromatograph for measurement. Details and variations on this technique are described in the following four references:
1. "Interim Method for the Sampling and Analysis of Priority Pollutants in Sediment and Fish Tissue" Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, Ohio, p 18 and 45-268, Aug. 23, 1977,
2. "Sampling and Analysis for Screening of Fish for Priority Pollutants," "Analysis of fish for Volatile Organics by Head Space Analysis", U.S. EPA, Environmental Monitoring and Support Laboratory, Cincinnati, Ohio p. 14, Aug. 23, 1977,
3. "The analysis of Fish for Volatile Organics by Head Space Analysis" U.S. Environmental Monitoring and Support Laboratory, Cincinnati, Ohio p. 21,
4. Going, "Priority Pollutant Removal from Mine Drainage" Final Report, MRI Contract 4409- L3, Industrial Environmental Research Laboratory, Office of Research and Development, EPA Cincinnati, Ohio.
These methods have several drawbacks. First, the chemical of interest may not readily disassociate from the sample to permit accurate measurement in the gas. Second, water and other volatile compounds frequently interfere with the detection of the compound of interest. If the compound being detected can form an azeotrope, further complications exist. Third, these techniques are only effective for very volatile compounds.
Another existing technique for measurement of trace organic compounds involves pentane extraction of organic compounds from fish as discussed by Pearson et al, Proc. Royal Soc. Lond. B, 189: p. 305-332 (1975). This technique has the disadvantage of only measuring compounds which are soluble in pentane, do not react with pentane, are released from the matrix by liquid pentane and do not participate in a chemical reaction with any other compound being extracted by the pentane.
Another standard technique for measurement of trace organic compounds is to purge and trap. According to this technique, the sample is heated and an inert gas is passed through the sample to "purge" volatile compounds from the sample. The gas containing the compounds is passed through a trap which adsorbs the compounds. One such adsorbent is activated charcoal. The adsorbent is then heated to elute the compounds from this trap into a gas chromatograph for detecting and measuring the compounds. One example of this technique is Murray, Analytical Chim. Acta, 65 p. 261-270 (1973).
The purge and trap technique also has certain drawbacks as different compounds have variable rates of adsorption on adsorbents. Furthermore, heating the sample may cause degradation of the compounds of interest. The compounds concentrated in the adsorbent may react with each other or degrade because they are in a different matrix than the one from which they were extracted. Also the compounds being tested may polymerize or react with other compounds present to give byproducts, thereby making it difficult to detect the correct compounds present and causing simultaneous detection of compounds which never were in the sample. While the purge and trap technique recovers a wide mix of compounds, it still fails to adequately recover many compounds.
This may be especially true when non-aqueous samples are analyzed. For non-aqueous samples recoveries are further complicated by any additional affinity for compounds of interest to the solid phase over the aqueous phase. Non-volatile compounds are particularly hard to extract and measure accurately using this technique.
Some of the problems with heating a sample and trapping the released compounds have been ameliorated by using a vacuum instead of heat to extract compounds. Examples of this technique are Easley et al, J. Assoc. Off. Anal. Chem., 64(3) p. 653-656 (1981) and applicant's earlier publication, Hiatt, Analytical Chemistry, 53: p. 1541-1543 (1981).
Improvements in the purge and trap method have been provided as described in Hiatt, Analytical Chemistry, 55: p. 506-516 (1983) and Hiatt, U.S. Pat. No. 4,600,559. These publications disclose a vacuum extractor with cold traps to condense and collect the compounds being measured. While such a system is more effective than conventional techniques, it is cumbersome with plural cold traps and does not readily lend itself to automation. Additionally, this and all other systems permit the measurement of compounds in the gaseous phase only and do not permit measuring the azeotrope phase, the condensed phase or the residue in the sample container. Thus the previous systems are limited in their capabilities.